Field of the Invention
The present invention relates to locks and more particularly to an apparatus for and method of re-keying a pin tumbler cylinder lock having tumbler pins, driver pins and at least one master pin without disassembly of the lock apparatus or removal or replacement of any master pins therefrom or therein.
Description of the Prior Art
The pin tumbler lock principle is widely used in builders hardware locks, padlocks and cabinet locks. A pin tumbler lock housing has a cylindrical main bore extending longitudinally therethrough to rotatably accommodate a cylindrical plug having a flange at its front end to limit its rearward movement relative to the housing. The plug has a keyway extending longitudinally therethrough at the bottom of the plug. A plurality of parallel and equally spaced cylindrical top pinways perpendicular to the main bore extend from the top of the housing into the main bore to align with correspondingly spaced cylindrical bottom pinways extending from the top of the plug to part way into the keyway. Retainers of various types secured to the rear end of the plug provide a minimum of end play between the plug and the housing when the lock is assembled. Each pinway extending from the top of the housing to part way into the keyway has within it a tumbler pin having a truncated conical bottom end that engages a truncated cut or bitting on the top edge of a key inserted in the keyway. The bitting positions the tumbler pin vertically in the pinway. Above each tumbler pin is a driver pin of sufficient height to block a shear interface between the plug and the housing when the tumbler and driver pins are bottomed in their pinway. Above each driver pin is a compression spring that biases the driver pin and the tumbler pin in a downward direction. The height of a tumbler pin is such that the interface between the tumbler pin and the driver pin is located at the shear interface by a properly selected bitting on a key inserted in the keyway. When the key bittings locate all such driver pin and tumbler pin interfaces at the shear interface, the plug is free to rotate and retract a bolt or latch by means of the surfaces of the retainer, or an extension thereof, acting on the bolt or latch.
Tumbler pin heights and bitting depths of the key are multiples of an increment established by the manufacturer. There are usually ten tumbler pin heights and ten corresponding bitting depths numbered zero through nine, zero designating the shortest tumbler and the shallowest bitting depth and nine designating the tallest tumbler and the deepest bitting depth. The increment is large enough to ensure that a key having one or more bitting depths shallower or deeper than corresponding tumblers will not permit the plug to rotate because of the normal clearance between the plug and the housing.
A key that is intended for use with an individual lock or a group of locks keyed alike is referred to as a change key. A key that will operate a group of locks, each of which is operated by its own unique change key, is referred to as a master key. Pin tumbler locks are masterkeyed by using short pins called master pins between the tumbler pin and the driver pin in a given pinway. A tumbler pin, a driver pin and any master pins between them can be referred to as a tumbler stack. The interface between a master pin and a driver pin usually determines the change key bitting, and the interface between the tumbler pin and the master pin determines the master key bitting. A plurality of locks can thus be set up to each operate with its own unique change key, yet all of the locks can be operated with the same master key.
For ease of reference, the locations of each pinway, and thus the location of the bitting for operating the tumbler stack in that pinway, are referred to as stations designated by the letters A, B, C, etc. with station A relating to the pinway that is closest to the front of the lock.
The necessity to re-key locks is an ongoing problem, particularly with a turnover of employees and tenants. Some concerns, such as banks, consider re-keying on a periodic basis to be a matter of good policy. Normally, re-keying the change key of a lock requires disassembly of the lock and removal and replacement of tumbler pins with tumbler pins of different heights if the lock is not masterkeyed. If masterkeyed, removal and replacement with different-height master pins has been required. Ideally, the delay in waiting for and the expense of a locksmith are to be avoided.
Attempts have been made to re-key locks by providing a slot in the plug for receiving a slide having eight holes for use with four pinways. When the lock is assembled, the extra or auxilliary holes are either empty, filled with master pins having a height that is equal to the full thickness of the slide or filled with master pins that are shorter than the full thickness of the slide. A set screw is used to move the slide in the slot into one of two positions to align two different sets of the holes with the pinways. Because of the different arrangement of holes and master pins in each of the two positions of the slide, a different change key is required to operate the lock for each position of the slide. However, without increasing the length of the lock, or disassembling the lock, the lock can be re-keyed for only two change keys.
Other attempts to re-key a lock to provide operation with more than two change keys have increased the length of the housing to provide more pinways in the housing than in a plug received in the housing. A set screw holds the plug in alignment with three different sets of the housing pinways, where each set has a different pin combination that requires change keys having different bittings. Although the lock can be re-keyed for use with any of the three different change keys, the increased length of the lock limits the situations in which the lock can be used.
Although also provided with a housing having an increased length, another re-keyable lock was provided with a spring biased plunger extending from the housing into a plug that was slidable in the housing for alignment with three different sets of pinways in the housing. A special key inserted into the keyway was used to operate the plunger to release the plug and allow it to slide rearwardly in the housing. The special key was easier to use than the set screw for re-keying the lock. However, unless the lock was disassembled it could be re-keyed for use with only three different change keys and the housing had an increased length to provide more pinways than the number of pinways in the plug.
Others have re-keyed a lock by using a special key having a bitting that locates a pin in the housing pinway to facilitate removal of the pin from the lock. The pin remains in the housing pinway when the special key and the plug are rotated 180.degree.. The removable pin is then transferred from the housing pinway into a slot formed in the special key. The special key and the removable pin are then removed from the lock. To enable the lock to be used with increased quantities of change keys, another special key is used to insert new removable pins into the lock, which requires careful handling of the very small removable pin.
Also in the past, locks have been keyed for operation using many keys, including, for example, a key for use only during construction. Special keys have been used to lock-out or prevent use of the construction key with the lock, while all of the rest of the original keys can operate the lock. However, the special key and the structure of the lock do not render the lock usable with only one of the many keys instead of the construction key that is locked-out.